Various processes using N,N′-dimethylethylenediamine as a starting material have been proposed for preparing 1,3-dialkyl-2-imidazolidinones; for example, reacting N,N′-dimethylethylenediamine with trichloromethyl chloroformate (JP-A 53-73561); reacting N,N′-dimethylethylenediamine with carbon dioxide (JP-A 57-175170); reacting N,N′-dimethylethylenediamine with phosgene in the presence of water and a dehydrochlorinating agent (JP-A 61-109772 and JP-A 61-172862); and reacting N,N′-dialkylethylenediamine with urea in a polar solvent (JP-A 7-252230). A known process for preparing N,N′-dialkylethylenediamines as a starting material such as N,N′-dimethylethylenediamine described above is based on ethylene dichloride and monomethylamine as described in JP-A 57-120570. The process, however, produces a large amount of salt contaminated with organic compounds as a byproduct, which may cause a difficult issue of disposal. J. Organometallic Chem., 407, 97 (1991) has described a process where ethylene glycol is reacted with monomethylamine in the presence of a homogeneous catalyst comprising ruthenium and triphenylphosphine. Recovery and recycle of a homogeneous noble metal catalyst is, however, industrially difficult. Therefore, a process using N,N′-dialkylethylenediamine as a starting material is not ideal for preparing 1,3-dialkyl-2-imidazolidinone.
In addition, there have been proposed reduction of 2-imidazolidinone and formaldehyde in the presence of a hydrogenation catalyst (JP-A 60-243071) and catalytic reduction of N,N′-hydroxymethylimidazolidinone dialkyl ether (JP-B 60-3299). These processes, however, employ a starting material derived from ethylenediamine. which may also cause the problem described above, and are impractically longer processes.
Alternative processes have been disclosed, including reacting an N-alkylmonoethanolamine and an alkylamine such as monomethylamine with carbon dioxide, an alkylamine alkylcarbamate or 1,3-dialkylurea (JP-A 57-98268); reacting ethylene glycol, carbon dioxide and monomethylamine at an elevated temperature under a higher pressure (JP-A 59-155364); and reacting alkylene carbonate with monoalkylamine (JP-A10-502917). These processes are one-step processes, and an N-alkylmonoethanolamine, ethylene glycol and an alkylene carbonate as starting materials can be readily prepared from an alkylene oxide. These processes are, therefore, noteworthy. These processes have a problem of production of N-alkyldiethanolamines as byproducts during preparing an N-alkylmonoethanolamine from ethylene oxide. JP-A 10-330366 has disclosed a process for preparing DMI by a one-pot reaction from ethylene oxide, which has a problems of a lower yield.
In these processes, a monoalkylamine as a starting material is disproportionated during a reaction to give disproportionation byproducts, i.e., ammonia, a dialkylamine and/or a trialkylamine. JP-B 1-15503 has disclosed a process where ethylene glycol is used as a starting material and unreacted materials containing a monoalkylamine is circulated and recycled in a reactor. In this process, ammonia as a byproduct is also circulated so that repeated circulation may increase ammonia, leading to increase of byproducts such as 1-alkyl-2-imidazolidinones and reduction in an yield of desired 1,3-dialkyl-2-imidazolidinones. Thus, this process has not been industrially available.